This invention pertains to a method of making molded hollow plastic bodies, having internal structures, such as radar reflectors, enclosed within a continuous envelope of plastic, and in which the finished article has no seams or vent holes to weaken it. The radar reflector marker buoy shown and described in my pending application Ser. No. 328,659, is typical of the type of molded article which might be made by the method of the present invention. Other devices such as navigational aids, and search-and-rescue aids might also be made by the present method.
The commercial fising industry has long used flotation devices to support fishing gear and to locate pots in crab and lobster fishing. Also, gill net fishing is conducted in navigable waters, and a method is required to prevent ships from running over the nets. One of the problems encountered by fishermen is that of locating the marker buoys when they return to the fishing nets or crab and lobster pots. Since most commercial fishing boats and larger ships are equipped with radar, it has become common practice to use radar reflectors inside the fishing buoys, which allow the radar to locate the buoys by the blip prodiced on the radarscope by the reflected echo. Heretofore, such radar reflectors have been enclosed within hollow spherical buoys by forming the buoys in two halves and then welding the halves together after placing the reflector inside the sphere. The only trouble with buoys made in this way is that the seam forms a line of weakness, which often causes failure of the plastic at that point when the buoy is pulled far underwater by tidal surges.
Another disadvantage of the prior radar-reflector buoys is that the size of the spherical fishing buoy limits the size of the radar reflector, with the result that the radar return is relatively weak. Anything that further weakens the signal may reduce the blip on the radarscope to the point where it is indiscernible. The radar reflector most commonly used at this time is a 3-plane, rigid corner cube, made of 3 mutually perpendicular panels of flat sheet aluminum, which define a cluster of eight outwardly facing tetrahedrons. If the reflector is partially submerged in water, or if it is tilted in certain ways, the radar return is minimized, and a weak blip results.
In addition to its application to fishing buoys, the invention also pertains to navigation aids, particularly in connection with low-maintenance, reliable radar reflecting units. Such radar reflecting floats, when used by the boating public, would provide an effective means for locating boats that are lost, stranded, or in distress, by rescue searchers operating from sea or air.